Carbon and its compounds Homologous Series - Alkanes CBSE Class 10 Chemistry Chapter 4 NCERT

Carbon and Its Compounds: Covalent Bonding, Nomenclature, and Functional Groups

Carbon is a unique element that forms the basis of all living organisms and millions of known compounds — more than all other elements combined. This exceptional ability arises from two properties: catenation (the ability to form bonds with other carbon atoms, creating long chains, branched chains, and rings) and tetravalency (carbon has four valence electrons, allowing it to form four covalent bonds). This chapter in CBSE Class 10 Science introduces students to the nature of covalent bonding, hydrocarbons, functional groups, IUPAC nomenclature, and important chemical properties of carbon compounds including combustion, oxidation, addition, and substitution reactions.

Covalent bonds are formed by the sharing of electrons between atoms, as opposed to ionic bonds which involve electron transfer. Carbon shares its four valence electrons with other atoms to achieve a stable octet configuration. A single bond involves sharing one pair of electrons (as in CH₄, methane), a double bond involves two pairs (as in C₂H₄, ethene), and a triple bond involves three pairs (as in C₂H₂, ethyne). Hydrocarbons are compounds of carbon and hydrogen only, classified as saturated (alkanes, with single bonds only, general formula CnH₂n₊₂) or unsaturated (alkenes with at least one C=C double bond, CnH₂n; alkynes with at least one C≡C triple bond, CnH₂n₋₂). Isomers are compounds with the same molecular formula but different structural arrangements — butane (C₄H₁₀) has two isomers: n-butane (a straight chain) and isobutane (a branched chain). The number of isomers increases rapidly with the number of carbon atoms.

Functional groups are specific groups of atoms within molecules that determine the characteristic chemical reactions of those molecules. The hydroxyl group (−OH) characterises alcohols (e.g., ethanol C₂H₅OH), the aldehyde group (−CHO) characterises aldehydes (e.g., ethanal CH₃CHO), the carboxyl group (−COOH) characterises carboxylic acids (e.g., ethanoic acid CH₃COOH, commonly called acetic acid), and the amino group (−NH₂) characterises amines. IUPAC nomenclature provides a systematic method for naming organic compounds based on the longest carbon chain and the functional group present. Key reactions include combustion (all hydrocarbons burn in oxygen to produce CO₂, H₂O, and heat — this is why they are used as fuels), addition reactions (unsaturated hydrocarbons add hydrogen in the presence of a catalyst like palladium or nickel — this is how vegetable oils are hydrogenated to make vanaspati ghee), substitution reactions (saturated hydrocarbons react with chlorine in the presence of sunlight: CH₄ + Cl₂ → CH₃Cl + HCl), oxidation (alcohols oxidise to carboxylic acids using oxidising agents like alkaline potassium permanganate), and esterification (an alcohol reacts with a carboxylic acid in the presence of concentrated sulphuric acid to form an ester — sweet-smelling compounds used in perfumes and flavourings). Soaps are sodium or potassium salts of long-chain fatty acids, formed by the saponification (hydrolysis) of esters with NaOH. Soaps form micelles around dirt particles, with the hydrophobic tails embedding in grease and the hydrophilic heads facing water, allowing the dirt to be washed away. Soaps do not work well in hard water (which contains calcium and magnesium ions) because they form an insoluble scum — synthetic detergents were developed to overcome this limitation.

• Carbon's catenation and tetravalency allow it to form millions of compounds through covalent bonding.
• Hydrocarbons: alkanes (CnH₂n₊₂, single bonds), alkenes (CnH₂n, double bonds), alkynes (CnH₂n₋₂, triple bonds).
• Functional groups determine chemical behaviour: −OH (alcohols), −CHO (aldehydes), −COOH (carboxylic acids), −NH₂ (amines).
• Key reactions: combustion (fuel burning), addition (hydrogenation of oils), substitution, esterification, and saponification.
• Soaps are sodium salts of fatty acids; they clean by forming micelles. Detergents work in hard water where soaps fail.